c-g-designs

IV)-ACTION DESIGN.

CONCEPTION OF SINGLE SHOT  MATCH ACTIONS

3-RAW MATERIALS, TREATMENTS and FINISHES.

As soon as the specification data list for a given action, and  project components has been established, the first question to answer will be what material and alloy  will be best suited to make the part from?.. Determine also what treatments needed for the established characteristics. This is often a difficult choice.

Lets take the example of a receiver:

Specification:

--Impact and wear resistance.

--Machineablity:

--Ability to obtain close tolerances and finishes.

--Aptitude to the heat treatments necessitated to obtain the mechanical properties required.

--Need the finally machined part able to be submitted to the required heat treatments above without warping, or :

--Does the material chosen need a further finishing to be performed after heat treatment to eliminate possible warpings?.  (grinding or honing for instance, as straightening after treatment being prohibited for such a part).

--Aptitude to final polishing. surface protection and eventually cosmetic treatments (for instance, a high nickel alloyed steel does not blue too well but polishes very nicely).

--The finally chosen alloy must also be easily available in the form, dimension and condition required, this being diameter for bar stock and the right condition for machinining (annealed or pre-hardened condition for instance).

In the structural and tool steels range, my choice for most functional parts has always gone first to the European 42NiCrMo16 (werkstoff Number 1.6773, offered here by the major steel mills, for Instance  Boehler brand name being K600).

This is a tough high-alloyed tool steel 4%Nickel, 2%Chromium, 1%Molybdenium,  hardening at 51-52 hR’C’ (185 kgs/mm² or 263000 PSI). It is characterized by its absolute total dimensional stability under heat treatment.. Machines well and is high-impact and wear resistant. BUT, high-specification qualities having a cost, this alloy is expensive and this reflect significantly in the part final cost.

For bolts, I find preferable to use the same alloy and treatment as for the receiver (42NiCrMo16) full-hardened to 51-52 hR’C’ as well.

Use of surface hardened steel, such as 20MoCrS4 (AISI 6820 or WNr 1.7323)  for bolts can be used, but this low carhon steels and its required treatments (case hardening) does not guarantee the necessary dimensional stability and require a further finish after treatment. The nitrided coat is also brittle and is reduced in thickness after grinding..

Personally, I consider using for the bolts harder surface-hardened material than the receiver is a source of issues. Full hardened identical materials is my proven solution.

Other parts: Each component could call for a specific alloy, but (except for FP tips) allow to more flexibility of choice than receivers and bolts. It is always better to choose the full hardened (quenched) part instead as carbo-nitrided ones, a surface-hardening process for milder steels in which the surface carbon content is increased to render it hardenable,  Melonite QPQ being a typical example among others less advanced surface hardening processes.

A common alloy used here is the 40CrMnMoS8 (W/N 1.2311 or AISI P20+S). This is a free machining tool steel, apt to full hardening, and available in small diameter ground or cold draw round rods, allowing in many cases a direct dimension part with the minimum of machining. This is my primary choice for most small parts, except firing pin tips as expressed above.

Surface finishes. There is several aspects to the surface finish of Receivers and Bolts:

-Corrosion protection

: Blueing, electroless nickel plating, electro-chemical matt chrome plating, PVD coating, Me-DLC coating (Diamond-Like-Coating or Tribo-coating,) Ni-PTFE coating, Cerakoting…..

-Wear resistance; Electroles plating, PVD coating, Me-DLC, hard chrome plating (bolts) Ni-PTFE.

-Friction reduction; Me-DLC, PVD coating, Hard Chrome, Ni-PTFE.

-Aspect

: PVD coating (shiny gold, old silver, blue-grey, black..), Me-DLC (black), Blueing, Electroless Ni plating (matt silver), Ni-PTFE, Cerakoting…

R.G.C